Group I Metabotropic Glutamate Receptors and Epileptogenesis

描述(由申请人提供)： 创伤性脑损伤、中风或癫痫持续状态后癫痫的发展是一个涉及许多机制的过程，这些机制为癫痫的预防提供了靶点。在所有这些癫痫病因中，一个可能很重要的机制是谷氨酸过度释放和代谢性谷氨酸受体(MGluRs)的激活。我们还没有开发出预防癫痫发展的疗法，特别是在脑外伤后，我们的提案评估了潜在的预防疗法。该计划的目标是通过改变mGluR激活的效果来开发潜在的治疗方法来防止癫痫发生。我们发现，用选择性激动剂二羟基苯甘氨酸(DHPG)激活I组mGluRs会导致海马兴奋性的长期变化，表现为自发发生的发作间期(发作间)和发作(发作样)活动。在过去的资助期间，我们已经证明了阻断I组mGluRs可以减缓点燃，这是一种癫痫发生的模型。我们的发现产生了新的研究问题，我们在当前的提案中解决了这些问题。我们的第一个假设是，激活I组mGluRs优先增加反复出现的兴奋性突触网络活动，并导致海马CA3区持续的癫痫样活动。我们的第一组具体目标将解决短暂接触DHPG后CA3区突触生理学的变化。我们将：1)表征DHPG暴露后自发发生的抑制性突触后电流(IPSCs)和兴奋性突触后电流(EPSCs)的频率和幅度，并将其与对照神经元活动进行比较；2)评估在没有抑制的情况下自发发生的EPSCs和在没有突触兴奋的情况下自发发生的IPSCs；以及3)确定与DHPG暴露相关的微型IPSC和EPSC频率和幅度的变化。我们的第二个假设是，I组mGluRs引起的长期变化是Hmer 1a产生的结果，Hmer 1a是一种被癫痫发作上调的蛋白质，而I组mGluRs的功能发生了变化，从而在没有谷氨酸的情况下激活了阳离子电流。我们的初步数据表明，荷马1基因敲除(KO)小鼠对DHPG诱导的癫痫样反应具有抵抗力。因此，我们将确定荷马1KO小鼠是否会出现与DHPG暴露相关的细胞膜性质的变化，并将确定将荷马1KO小鼠与Hmer 1a转导是否可以重新建立与DHPG诱导癫痫样活动有关的野生型表型。我们认为，我们定义的在DHPG暴露后发生的变化，模拟了高浓度细胞外谷氨酸激活mGluRs时发生的变化，并且它们代表了阻止头部创伤、癫痫持续状态和反复发作后癫痫发展的治疗靶点。我们的实验结果将针对癫痫的新疗法和癫痫的发展，癫痫是经历过脑外伤的战斗退伍军人的主要发病率。

DESCRIPTION (provided by applicant): The development of epilepsy following traumatic brain injury (TBI), stroke, or status epilepticus is a process that involves many mechanisms that provide targets for the prevention of epilepsy. One mechanism that may be important in all of these causes of epilepsy is excessive glutamate release and activation of metabotropic glutamate receptors (mGluRs). We have not yet developed therapies to prevent the development of epilepsy, particularly following TBI, and our proposal evaluates potential prophylactic therapies. The goal of this program is to develop potential treatments to prevent epileptogenesis by altering the effects of mGluR activation. We have found that activation of group I mGluRs with the selective agonist dihydroxyphenylglycine (DHPG) results in long-lasting changes in hippocampal excitability manifest by spontaneously occurring interictal (between-seizures) and ictal (seizure-like) activity. In the past funding period, we have demonstrated that blockade of group I mGluRs can slow kindling, a model of epileptogenesis. Our findings have created new research questions, which we address in the current proposal. Our first hypothesis is that activation of group I mGluRs increases preferentially the recurrent excitatory synaptic network activity and results in persistent epileptiform activity in the CA3 region of the hippocampus. Our first set of specific aims will address changes in synaptic physiology of the CA3 region that follow transient exposure to DHPG. We will: 1) characterize the frequency and amplitude of spontaneously occurring inhibitory postsynaptic currents (IPSCs) and excitatory post synaptic currents (EPSCs) after DHPG exposure and will compare this with control neuronal activity; 2) evaluate spontaneously occurring EPSCs in the absence of inhibition and spontaneously occurring IPSCs in the absence of synaptic excitation; and 3) determine changes in miniature IPSC and EPSC frequency and amplitude that are associated with DHPG exposure. Our second hypothesis is that long-term changes induced by group I mGluRs are the result of production of Homer 1a, a protein up-regulated by seizures, and change in function of group I mGluRs so that a cation current is activated in the absence of glutamate. Our preliminary data indicate that Homer 1 knockout (KO) mice are resistant to the induction of epileptiform by DHPG. We will therefore determine if Homer 1 KO mice develop changes in membrane properties associated with DHPG exposure and will determine if a transduction of the Homer 1 KO mouse with Homer 1a can re-establish the wild type phenotype as relates to the induction of epileptiform activity by DHPG. We argue that the changes we define that occur following DHPG exposure, models what occurs when high concentrations of extracellular glutamate activate mGluRs, and that they represent a therapeutic target to block the development of epilepsy following head trauma, status epilepticus, and recurrent seizures. The results of our experiments will target new therapies for epilepsy and the development of epilepsy, a major morbidity for combat Veterans who have experienced TBI.